Add a dart:io WebSocket implementation (#1139)

pkgs/web_socket/README.md

@@ -1,2 +1,46 @@
-TODO: Put a short description of the package here that helps potential users
-know whether this package might be useful for them.
+[![pub package](https://img.shields.io/pub/v/web_socket.svg)](https://pub.dev/packages/web_socket)
+[![package publisher](https://img.shields.io/pub/publisher/web_socket.svg)](https://pub.dev/packages/web_socket/publisher)
+
+Any easy-to-use library for communicating with WebSockets that has multiple
+implementations.
+
+## Using
+
+```dart
+import 'package:web_socket/io_web_socket.dart';
+import 'package:web_socket/web_socket.dart';
+
+void main() async {
+  final socket =
+      await IOWebSocket.connect(Uri.parse('wss://ws.postman-echo.com/raw'));
+
+  socket.events.listen((e) async {
+    switch (e) {
+      case TextDataReceived(text: final text):
+        print('Received Text: $text');
+        await socket.close();
+      case BinaryDataReceived(data: final data):
+        print('Received Binary: $data');
+      case CloseReceived(code: final code, reason: final reason):
+        print('Connection to server closed: $code [$reason]');
+    }
+  });
+
+  socket.sendText('Hello Dart WebSockets! 🎉');
+}
+```
+
+## Status: experimental
+
+**NOTE**: This package is currently experimental and published under the
+[labs.dart.dev](https://dart.dev/dart-team-packages) pub publisher in order to
+solicit feedback.
+
+For packages in the labs.dart.dev publisher we generally plan to either graduate
+the package into a supported publisher (dart.dev, tools.dart.dev) after a period
+of feedback and iteration, or discontinue the package. These packages have a
+much higher expected rate of API and breaking changes.
+
+Your feedback is valuable and will help us evolve this package. For general
+feedback, suggestions, and comments, please file an issue in the
+[bug tracker](https://github.com/dart-lang/http/issues).

pkgs/web_socket/example/web_socket_example.dart

@@ -1,3 +1,41 @@
-void main() {
-  // TODO: add an example.
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:web_socket/io_web_socket.dart';
+import 'package:web_socket/web_socket.dart';
+
+const requestId = 305;
+
+/// Prints the US dollar value of Bitcoins continuously.
+void main() async {
+  // Whitebit public WebSocket API documentation:
+  // https://docs.whitebit.com/public/websocket/
+  final socket =
+      await IOWebSocket.connect(Uri.parse('wss://api.whitebit.com/ws'));
+
+  socket.events.listen((e) {
+    switch (e) {
+      case TextDataReceived(text: final text):
+        final json = jsonDecode(text) as Map;
+        if (json['id'] == requestId) {
+          if (json['error'] != null) {
+            stderr.writeln('Failure: ${json['error']}');
+            socket.close();
+          }
+        } else {
+          final params = (json['params'] as List).cast<List<dynamic>>();
+          print('₿1 = USD\$${params[0][2]}');
+        }
+      case BinaryDataReceived():
+        stderr.writeln('Unexpected binary response from server');
+        socket.close();
+      case CloseReceived():
+        stderr.writeln('Connection to server closed');
+    }
+  });
+  socket.sendText(jsonEncode({
+    'id': requestId,
+    'method': 'candles_subscribe',
+    'params': ['BTC_USD', 5]
+  }));
 }

pkgs/web_socket/lib/io_web_socket.dart

@@ -0,0 +1 @@
+export 'src/io_web_socket.dart' show IOWebSocket;